1. Field of the Invention
The present invention relates to a plating apparatus which performs an operation of plating on a processing surface of a workpiece such as a wafer as a device fabrication step and a method of manufacturing a semiconductor device by such a plating apparatus, and more particularly to a plating apparatus suitable for more uniformly plating on a processing surface and a method of manufacturing a semiconductor device.
2. Description of the Related Art
In recent years, a plating step in a semiconductor manufacturing process or a liquid crystal device manufacturing process has come to be used more often than a reaction process which is performed in a vapor phase state as the microfabrication required in manufacturing semiconductor devices or liquid crystal devices is advancing.
In such a plating step, it is significant to ensure the quality of a plated coating and the uniformity of a plated coating thickness on a surface of the workpiece in order to control the quality of semiconductors or the like to be manufactured.
For example, a step of copper plating on a surface of a processing wafer will be described. To plate copper on the processing wafer surface, a conductive seed layer, which makes a cathode for electrolytic plating and also a seed for plating, is previously formed on the pertinent surface.
The processing wafer surface on which the seed layer is formed is soaked in a plating solution bathe so to come into contact with, for example, a copper sulfate based plating solution. And, electrical conductors (cathode contacts which will be simply called contacts) are contacted to the seed layer via an outer periphery of the wafer to supply an electric current for the electrolytic plating. In the plating solution bathe, an anode made of, for example, phosphorus-containing copper is disposed in a state soaked in the plating solution.
Employing the above configuration, an electric current is supplied between the cathode and the anode to make reduction deposition of copper on the cathode which was initially the seed layer, thereby plating copper on the seed layer. When plating, the wafer is mostly spun about its axis in order to form a more uniform plating on the processing surface. Thus, even if a flow of the plating solution in the plating solution bathe is not uniform, it is made averaged, and plating is uniformly made on the surface.
However, this improvement of the plating process for the uniform plating on the surface is helpless against nonuniform plating which results from a contact resistance between the contacts and the wafer. It is a natural consequence because the contact between the circumferential edge of the wafer and the contacts is fixed at certain points and the wafer is spun together with the contacts in the contacted state. Thus, among the contacts which are in contact with the peripheral edge of the wafer, those having a smaller contact resistance have better conductivity with the wafer, but those having a high contact resistance have poor conductivity with the wafer.
Plating is actively carried out and a thick coated layer is formed on portions of the wafer ranging from the contacts contacted with good conductivity to the center of the wafer as compared with portions of the wafer ranging from the contacts contacted with poor conductivity to the center of the wafer. In other words, the processing surface of the wafer is not plated uniformly because of variations in the contact resistance between the contacts and the wafer.
A cause of variations in the contact resistance may be degradation in the contacts themselves. Generally, a wafer holding member structure for sealing with a sealing material is adopted at the contact portions between the circumferential edge of the wafer and the contacts in order to prevent the entry of the plating solution. It is because the plating solution is acid and corrosive.
However, even if sealing is complete, the entry of the plating solution in the form of steam or mist into the contact portions cannot be prevented. Thus, the contacts may be corroded to some extent or the plating material may be defectively deposited on the contacts, resulting is a change in their surfaces. Thereby, variations may be caused in the contact resistance of the contacts.
With the increase in diameter of the wafer in these years, a contact member itself is also becoming large in size, and the number of its contact points is many. It is becoming difficult to provide a constant contact resistance to each of the contact points by uniformly pushing the wafer to such a single contact member.
As described above, the plating apparatus being used now tends to have variations in the contact resistance between the contacts and the wafer and has limitations in uniform plating on the processing surface.
The present invention has been achieved in view of the circumstances described above, and it is an object of the invention to provide a plating apparatus and plating method which can plate more uniformly on a surface of a workpiece.
To achieve the aforementioned object, the plating apparatus according to the present invention has a plating solution bathe which can hold a plating solution and is provided with a first electrode held in a state soaked in the held plating solution; a workpiece holding mechanism which holds a workpiece to contact its processing surface to the plating solution; and a contact member which is disposed in the workpiece holding mechanism and electrically contacted to the circumferential edge of the workpiece so to form a conductive layer on the workpiece surface, which is in contact with the plating solution, as a second electrode; the contact member being divided along the circumferential direction of the workpiece to be electrically contacted.
As the contact member is divided along the circumferential direction of the workpiece, it is possible to adjust an electric current for the plating operation for each section of the contact member even if a contact resistance of the respective sections of the contact member with the workpiece is variable.
Specifically, when the contact member has a relatively high contact resistance, it suffers a voltage drop because of its contact resistance, and the plating electric current lowers accordingly. In such a case, the electric current is increased by raising a voltage applied during the plating operation via the contact member or the electric current for the plating operation via the contact member is directly increased.
Thus, the electric current for the plating operation can be made constant to each contact member, and as a result, the plating is uniformly made on the processing surface.
A method of manufacturing a semiconductor device according to the present invention employs a plating apparatus comprising a plating solution bathe which can hold a plating solution and is provided with a first electrode held in a state soaked in the held plating solution; a workpiece holding mechanism which holds a workpiece to contact its processing surface to the plating solution; and a contact member which is disposed in the workpiece holding mechanism and electrically contacted to the circumferential edge of the workpiece so to form a conductive layer on the workpiece surface, which is in contact with the plating solution, as a second electrode; the contact member being divided along the circumferential direction of the workpiece to be electrically contacted. This method comprises; holding the workpiece by the workpiece holding mechanism, bringing the processing surface of the held workpiece into contact with the plating solution, and plating on the processing surface while controlling the plating electric current passing through each divided section of the contact: member.
According to this method of manufacturing a semiconductor device, it is possible to uniformly plate on the processing surface by the same operation as the aforementioned plating apparatus.